David Waters

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Neutrino Astronomy General Overview Future
Prospects
David Waters University College London
Thanks Amy Connolly, Subir Sarkar
APP UK Conference, Oxford, 19th June 2008
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Outline

• Why Neutrino Astronomy ?
• Potential Sources of High-Energy Cosmic Neutrinos
• Detection Techniques
• Some Pioneering Experiments
• Where Next ?

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Truth in Advertising

• Only two extra-terrestrial neutrino sources have
  ever been observed

SN1987A
Solar-? Image (Super-K)

• Both had a profound impact on astroparticle
  physics.
• Neutrino astronomy awaits its true first-light.
  All you will see here are limits.
• But, there is very good reason to think we are
  getting close

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Particle Physics at Extreme Energies
Centre of Mass Energy (GeV)
Cosmic-Ray Spectrum Credit R. Engel

• Cosmic rays probe particle physics at ECM gtgt
  ELHC.
• Even simple observables (e.g. ?tot) can be used
  to search for new physics.
• Neutrinos could provide a particularly clean
  probe compared to hadrons.

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Multi-Messenger Astronomy
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Astrophysical Neutrino Sources

• What fluxes from astrophysical sources can be
  expected in general ?

Fraction of CR primary energy converted to
neutrinos
From rate of UHE CR's (1019-1021 eV)
Hubble time

• Many qualifications and caveats.
• Can be evaded if
• sources are optically thick
• neutrinos from other sources (top-down)

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Cosmogenic Neutrinos
GZK mechanism
ETHRESH. 6 ? 1019 eV

• Uncertainties in flux calculations
• UHECR luminosity ?CR(local) ? lt?CRgt
• injection spectrum
• cosmological evolution of sources
• IRB optical density of sources

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Cosmogenic Neutrinos

• Caveats
• Does the primary cosmic ray spectrum show
  evidence of the GZK cut-off ?
• Perhaps the UHECR sources themselves cut-off
  around the GZK energy cosmic conspiracy. Most
  assume a cut-off substantially higher 1021-1022
  eV (Hillas).
• Composition of the primary cosmic rays ?

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Connections with other Fields

• Astrophysics
• ?-Ray Astronomy
• Highest Energy CR's

n-Astronomy
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Cosmic Ray Neutrino Detection Methods
?
incoming neutrino
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Target Media

• Targets
• Ice
• Water
• Atmosphere
• Salt
• Lunar regolith

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Target Media
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Optical Cerenkov

• Similar to detection techniques used in
  low-energy experiments (Super-K).
• The only technique with a proven capacity to
  detect (atmospheric) neutrinos.
• Backgrounds CR muons (downward) atmospheric
  neutrinos (upward).

• Muon tracking
• Effective volume gtgt instrumented volume (_at_ E such
  that R? gtgt Sdetector)
• Excellent pointing accuracy.
• Relatively poor energy resolution.

• Cascade detection
• Effective volume instrumented volume.
• Poor pointing accuracy.
• Relatively good energy resolution.

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Optical Cerenkov
figure of merit for cascade detection

• Detector capabilities vary but broadly comparable
  between ice water
• Energy thresholds ranges
• Pointing resolutions
• Deployment operational difficulties

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Amanda-II
USA, Germany, Sweden, Belgium, Venezuela
South Pole
AMANDA

• Amanda II (2000)
• 19 strings
• 677 optical modules
• 400 m high
• 200 m wide
• VEFF O(0.01) km3 (cascades)
• 8 PMT's

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Amanda-II Physics Results
Point Source Search (2004) 607 days, median-E? ?
1.3 TeV No point sources identified
Diffuse Flux Search (2007) Consistent with
atmospheric-?s No evidence for cosmic diffuse
flux

• Plus many others
• Terrestrial WIMP searches.
• Atmospheric neutrino flux measurements out to
  high energies.
• Cosmic ray composition studies (in conjunction
  with surface arrays).
• Supernova watch.

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Ice Cube
USA, Germany, Sweden, Belgium, UK (Oxford), New
Zealand, The Netherlands, Venezuela

• Need a bigger detector
• 1 km3 volume 70 ? Amanda II
• 70 strings 1500-2500m deep 160 tanks (IceTop)
• 40 strings 80 tanks already deployed
• Construction to be completed in 2011

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Underwater Detectors
Deep Med. Sites
ANTARES
NEMO
NESTOR
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ANTARES

• Antares
• All 12 physics lines installed.
• 1 instrumentation line (environmental sensors,
  beacons, cameras, hydrophones)
• 0.1 km2 surface area.
• Significant UK input, e.g. optical beacons.

Feb-May 2007

• Clear signal for upwards going muons neutrino
  candidates.
• Data collection and analysis in progress.

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KM3Net

• EU ESFRI roadmap project.
• 40 institutions from 10 European countries
• UK Aberdeen, Leeds, Liverpool, Sheffield.

• 3 year, 20M design study for a km3 detector in
  the Mediterranean.
• Broad scope physics studies, detector design
  and site investigations.
• Conceptual Design Report delivered in April 2008
  TDR by end of 2008.
• Competitive with and complementary to IceCube.

LED beacon development - building on Antares
work. (Sheffield)
Fast simulation for detector configuration
studies (Liverpool)
Physics studies - building on data analysis
experience (Leeds)
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UHE GZK Neutrinos

• How big does our detector need to be to see the
  GZK neutrino flux ?

Flux 5 GZK neutrinos / km2 / yr in 2?
Interaction length 300 km _at_ 1018 eV
To detect 10 GZK neutrinos per year, we need to
have a sensitive volume of 100s km3.
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Extensive Air Shower
Pierre Auger Observatory ? Johannes

• Neutrinos at Auger
• Distinguish late (?) from early (h) showers for a
  given atmospheric depth using
• timing information
• pulse shape information
• Detect ?-decay showers from Earth-skimming
  neutrinos

??
In 1 full-array-year of data, Auger find no such
events and place a very competitive limit. See
summary.
New ! 2007/8
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Radio Emission Principle

• First described by Askaryan (1961).
• Expected 20 net negative co-moving charge
  excess (Zmacro) in UHE shower development due to
  
• Ionisation ? e- ? ?? e-
• Annihilation e e- ? ?
• Cerenkov radiation from Zmacro for v gt clocal .
• Radiation is coherent for

? gt Dshower O(10) cm
f 100 MHz few GHz

• Target requirements
• radio transparent
• instrumentable
• quiet

• Candidates
• ice
• dry salt
• sand / lunar regolith

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Radio Emission Proof of Principle

• Demonstrated for
• sand
• salt
• ice

COHERENCE
Target
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Pioneering Radio Experiments
FORTE (97-99)
RICE (99-present)
GLUE (99)

• Antenna array in south-polar ice.
• Sensitive in range 0.2-1 GHz
• Threshold 1016 eV

• Radio telescope.
• Target lunar regolith (moon-skimming neutrinos)
• High threshold 1011 GeV

• Satellite radio antenna
• Target Greenland ice sheet
• Very high threshold 1013 GeV

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Radio Ice Cerenkov Experiment
USA

• 20 dipole receivers in South Polar ice.
• Scattered within 200m ? 200m ? 200m cube.
• Threshold 1016 eV
• Effective volume 1 km3 _at_ 1018 eV
• Anthropogenic noise reduction through event
  reconstruction.
• Refractive effects measured in situ.
• Attenuation length gt array size.
• Sets competitive limits at GZK energies.

effective volume
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ANtarctic Impulsive Transient Antenna
USA, UK (UCL)
Solar Panels
M. Rosen, Univ. of Hawaii
ANITA Gondola Payload
Antenna array
Cover (partially cut away)
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Acoustic Emission Principle
Mechanism first described by Askaryan (1957)
Hydrodynamical emission of tracks of ionising
particles in stable liquids.
fast thermal energy deposition
slow heat diffusion
Temperature or Volume
D
Time (arbitrary units)
?t
h
h
(10-20 kHz for water)
coefficient of thermal expansivity
specific heat capacity
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Acoustic Emission Proof of Principle
More recent work (Erlangen, Zeuthen) has
confirmed this picture for both water and
ice-targets
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Study of Acoustic UHE Neutrino Detection
USA

• 7 hydrophones in a larger US navy array
  instrumented with 180 kHz ADC's.
• Warm water expansive but noisy.

SIGNAL ?
BIO easy to reject ?
Need well calibrated phase response
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Study of Acoustic UHE Neutrino Detection
USA

• Multi-phone coincidence requirements and fiducial
  volume cuts remove the remaining multi-polar
  background.

Detection contours log10E (GeV) 11-16
195 days livetime

• Thresholds too high small effective volumes at
  GZK energies.
• Fundamental limits (hydrophone sensitivity, noise
  floors) not yet reached.
• A lot of scope for
• finding quieter ocean volumes
• optimal hydrophone arrangement
• far larger hydrophone arrays

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IceRay

• Embedded detectors have lower energy thresholds,
  better for GZK (cf. RICE)
• Co-detection in different modes will provide the
  definitive signature of UHE-?s.
• Ice is the only medium feasible for all three
  optical, radio and acoustic.

• Radio antennae could be on surface or at depth.
• A small array of 18-36 stations could be
  operational by 2012 and would detect 4-8 GZK
  neutrinos/year.
• A larger array could feasibly detect O(100) GZK
  neutrinos/year ? physics astronomy !

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Summary of Results
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Conclusions/Roadmap
What might happen next ?
IceCube starts to see ?-sources
ANITA/AUGER see first GZK ?s
PeV energy ?-astronomy
Ultra-high energy ?-astronomy
physics, sources etc.
detection techniques (optical, acoustic)
Build KM3
Build IceRay

• After decades of steady progress, there is an
  excellent chance that neutrino astronomy will see
  its first light in the next few years.
• This is an exciting time - join us !

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The End